1. Field of the Invention
This invention relates to a fluid heat exchange system for heating and cooling, and more particularly, to an air-to-refrigerant heat exchange system for use in a heat pump using a non-azeotropic refrigerant mixture, in which the working fluid, or refrigerant, is always maintained in a counterflow heat exchange relationship with the conditioned fluid, or air, regardless of whether the system is operated in a heating or cooling mode. This invention also relates to a method for heating and cooling using a mixed refrigerant in which the refrigerant flows in only one direction through a heat exchanger in both heating and cooling modes of operation.
2. Description of Prior Art
In a heat pump, a space within a building is conditioned by transferring heat to or from a reservoir outside the building. An air-to-refrigerant heat pump employs two heat exchangers, one indoors and one outdoors. In the cooling mode, the indoor heat exchanger acts as an evaporator in the refrigerant cycle, cooling the conditioned space air as the warm air boils the refrigerant in the coil of the heat exchanger. In the heating mode, the indoor heat exchanger acts as a condenser in the refrigerant cycle, where the heat of compression as well as the heat input to the outdoor heat exchanger, from the outdoor air, is released to the conditioned space air. In a corresponding manner, in the cooling mode, the outdoor heat exchanger acts as a condenser in the refrigerant cycle, using the cooler outdoor air entering the heat exchanger from the environment to condense the refrigerant in the coil. In the heating mode, the outdoor heat exchanger acts as an evaporator in the refrigerant cycle in which the refrigerant in the coil is boiled by the warmer outdoor air entering the outdoor heat exchanger from the environment.
Known air-to-refrigerant heat pumps operate in a manner in which the refrigerant is in a counterflow heat exchange relationship with the conditioned and environmental air in only one mode of operation of the heat pump. This occurs because the role of the heat exchanger changes from evaporator to condenser, with a change in mode of the heat pump from cooling to heating. In such systems, the refrigerant directions in the vapor and liquid refrigerant lines are reversed by a reversing valve, resulting in a reversal of the flow of the refrigerant through the heat exchanger. In addition, air flow through the heat exchanger is in one direction only, regardless of the mode of operation of the system. As a result, efficiency of the heat transfer mechanism, and thus the heat pump, is compromised when operating in the mode in which the refrigerant and the air passing through the heat exchanger are in a concurrent flow relationship.
A heat exchange system which utilizes counterflow heat exchange to transmit the heating and cooling effects between two separate fluid streams by a heat pump is known from German reference 2,610,463. The heat pump employs a circuit having an evaporator, compressor, condenser and a throttle valve. Both the evaporator and the condenser are utilized for heat exchange with a separate fluid stream. In one mode of operation, the fluid stream is brought into counterflow heat exchange contact with the refrigeration circuit upstream of the evaporator between the condenser and the throttle valve. The fluid stream leaving the condenser is brought into heat exchange contact with the fluid stream entering the condenser. However, if the mode of operation is changed, the counterflow heat exchange relationship between the fluid stream and the refrigerant in the refrigeration circuit is no longer maintained.
German reference 2,931,147 teaches a heat pump with two compressors having two parallel circuits for extracting and discharging heat from a fluid connected by a common heat exchanger.
U.S. Pat. No. 4,262,493 discloses a heat pump with an outdoor heat exchanger having a plurality of refrigerant flow circuits covering a major portion of the air flow surface of the exchanger, and a separate refrigerant flow circuit covering the remaining portion of the air flow surface of the exchanger. A refrigerant expansion and check valve are arranged to permit refrigerant flow to be reversed, depending on whether the unit is operated in a cooling mode or a heating mode. However, a counterflow heat exchange relationship between the air and refrigerant is provided in only one mode of operation.
U.S. Pat. No. 4,524,587 teaches a rotary inertial thermodynamic absorptive system in which fluid flow is stabilized by controlling the impedances to fluid flow in the system such that the overall pressure drop of the fluid flow in the system is made to increase with increasing fluid flow rate. In one embodiment, overspill/underspill barriers in the absorption and desorption chambers of the disclosed device are utilized to provide counterflow heat exchange within the system.
None of the previously discussed prior art teaches a heat exchange system for an air-to-refrigerant heat pump in which the refrigerant and the air are maintained in a counterflow heat exchange relationship in both the heating and cooling mode of operation.